The high-resolution scanning apparatus that constitutes the present invention relates generally to methods and apparatus for converting images recorded on paper and film into digital data so that the images can be conveniently communicated to other locations and processed by digital computers. More specifically, the high-resolution scanning apparatus has to do with mechanisms that systematically scan an image-containing medium thereby enabling electronic circuits to extract the information content of the medium by measuring either the reflectivity or the transmissivity of the medium as a function of the two coordinates that identify points in the plane of the medium.
The development of personal computers with the computational power to process imagery has stimulated a demand on the part of illustrators, photographers, graphic artists, and others whose work is benefited by the computer manipulation of imagery for scanning apparatus that can convert the imagery of photographs and transparencies into digital data that can be handled by computers.
Scanning apparatus consists of a source of light which illuminates the image-containing medium, an optical system that images picture elements ("pixels") of the medium on light detectors, and a transport mechanism which moves the light source, the optical system and the light detectors along a predetermined path thereby obtaining measures of reflectivity or transmissivity of the medium throughout the area of the medium.
A performance parameter of considerable interest is the scanner resolution--how far apart must the pixels be for the scanner to measure the light emanating from a particular pixel. The fundamental limitation of resolution in present-day scanners is the precision of the transport mechanism. Typically, the transport mechanism in today's scanners consists of a screw- or belt-driven carriage moving along a guide rail. The driving means is quite often a stepping motor. The position of the carriage along the rail is obtained by counting the number of steps by the stepping motor.
The precision with which the position of a platform can be established in transport mechanisms of this type is limited by frictional effects, temperature effects, the difficulties of manufacturing ultra-precise parts, and material properties. These limitations appear to limit the resolution of scanners that utilize this type of transport mechanism to something like 2000 dpi (dots per inch).
Thus, while the realizable resolution of photographic materials can be 10,000 dpi or more, the resolution of the great majority of scanners presently on the market is less than 2000 dpi. The efficiency and economy of computer processing of imagery is thereby not available to those who wish to retain the high resolution of their photographs and transparencies during processing.
For example, there exists a large volume of data that has been archived on film and requires computer processing for publishing, electronic access and research. Much of this historical film has been reduced up to 52 times and to properly recover this information in a digital format, the scanner must have a resolution of at least 10,000 dpi.
The demonstrated usefulness of computer processing of imagery, the availability of high-resolution of photographic materials, and the growing population of graphic artists who wish to optimally meld the photographic and electronic technologies together for their benefit and the benefit of their clients has created a need for reasonably-priced scanning apparatus with resolutions of 10,000 dpi or more.